The invention relates to a variable-length connecting element for transmitting traction or pressure forces from and to assemblies connected to the free ends of the connecting element by means of fastening elements. The connecting element of this kind is preferably of rod-shaped design.
It is known practice to manufacture rod-shaped and variable-length connecting elements, hereinafter referred to as link rods, from a metal rod, the free ends of which are, for example, provided with threads having opposite directions. Fastening elements having, for example, an eye surrounding a bolt or an axle, can be screwed onto these threads.
Link rods are used, for example, for actuating switching and control elements for air routing in internal-combustion engines, e.g. in intake systems. The link rod connects a lever arm connected to a stepping motor with a shaft located in the intake manifold of the vehicle for controlling the timing angle of the valve flaps fastened to the shaft. The position of the stepping motor adjusts the timing angle of the flaps as required. The flaps determine the degree of swirl of the air and thus affect the emission characteristics and fuel consumption of the engine. The flaps must be adjusted to a certain position during assembly. This positioning is achieved by way of the adjustable link rod.
It must be possible to set the link rod to different lengths, in order to be able to balance out tolerance fluctuations between the components, compensate for play occurring between the components and be able to use these as universally manufacturable components with different engine geometries. In the simplest version, the length is adjusted by turning the metal rod, thus axially displacing the fastening elements mounted on the threads at the ends. Lock nuts can additionally be provided on the threads. Accordingly, rotary movement is required for fixing and alignment. In confined engine compartments, it may be difficult to gain access, with the result that this rotary movement cannot be performed without problems. In addition, it is usually only necessary to adjust the position of one fastening element. However, the rotary movement acts on both of the opposite threads provided on the ends, meaning that the end not requiring adjustment is also displaced. In this way, undesirable forces act on the assemblies connected by the link rod. This is particularly critical in relation to the sensitive stepping motor. Moreover, it is difficult, or even impossible in confined spaces, to obtain definitively reliable assembly, i.e. to achieve the necessary torque for fixing. The metal rod is usually designed as a metal casting of high weight. This contradicts the targeted reduction of weight in the automotive sector. Finally, the fixing of the fastening elements on the rod is a complex and time-consuming process.
The invention is based on the technical problem of designing a connecting element of the kind defined in the generic part of claim 1 that is lighter and can be assembled more accurately.
According to the invention, this technical problem is solved in that the connecting element is essentially of two-part design, having a receiving element and a plug-in element that can be inserted into the receiving element in a manner at least permitting longitudinal displacement and that can be fixed in the receiving element in a desired position relative to the receiving element.
As a result of the design according to the invention, the link rod with the two fastening devices can be fastened to the connecting elements and pushed together or pulled apart until the desired axial length is obtained. A fixing element locks the plug-in element in this position in the receiving element. In the preferred configuration, the fixing element is designed as an easily manufactured metal slide. As an alternative, it can also be designed as a metal ring with teeth on the flanks.
The receiving element and the plug-in element are preferably manufactured in the form of plastic injection mouldings, this not only resulting in a reduction in weight, but also offering resistance to aggressive media.
The plug-in element is customarily guided and mounted in the receiving element without play and in a manner allowing longitudinal displacement. In this context, snap-in devices formed between the receiving element and the plug-in element can prevent the components from unintentionally falling apart. When supplied, the elements are snapped together, but not adjusted, and are far easier to assemble than the rods known from the prior art. This advantage becomes particularly apparent in view of the higher degree of automation of mass production.
In the case of components that are critical in terms of movement, it is also desirable to prevent rotation of the receiving element relative to the plug-in element. It is thus sensible for the plug-in element to be guided in the receiving element in non-rotating fashion. This can be achieved, for example, by designing the receiving element with a non-round inner contour, into which the complementary, non-round outer contour of the plug-in element can be inserted in sliding fashion. An elliptical inner contour of the receiving element and an elliptical outer contour of the plug-in element are used with preference. If rotation of the two elements relative to each other is wanted, they can be provided with a round inner contour of the receiving element and a round outer contour of the plug-in element, so that the plug-in element can rotate in the receiving element.
In the preferred configuration, fixing of the plug-in element in the receiving element is achieved by using a fixing clip, which can be inserted in the desired position between the plug-in element and the receiving element. The fixing clip is slid into a receiving opening provided on the side of the receiving element for fixing in the desired position. Assembly and setting of the length can thus be performed with one hand without requiring tools. The fixing clip establishes both a non-positive and a positive connection between the plug-in element and the receiving element, as the fixing clip is provided with cutting edges that cut into the plastic during insertion. Seen in the cross-sectional view, the fixing clip is preferably designed as a U-shaped metal clip with two longitudinal limbs, running in the longitudinal direction and aligned parallel to each other, and a transverse limb connecting the longitudinal limbs.
Accordingly, the invention also relates to a fixing clip for fixing, and preventing relative movement between, a plug-in element manufactured from a plastic material and a receiving element manufactured from a plastic material into which it can be inserted, said fixing clip being capable of insertion between the elements in the desired position between the receiving element and the plug-in element in order to guarantee at least a positive connection. The link rod and/or the fixing of the relative positions of the receiving and plug-in elements by a fixing clip can, of course, also be used for other elements, such as for connecting the door knob with the door-opening mechanism. Also, the connecting element need not necessarily be of rod-shaped design. Using the fixing clip, it is also possible, for example, for several plug-in elements to be inserted in a receiving element of star-shaped design for accommodating several plug-in elements, or in an essentially Y-shaped receiving element. Accordingly, the essential aspect is the relative fixing of one plastic part in another by the fixing clip.
In order to guarantee particularly firm fixing of the fixing clip between the receiving element and the plug-in element, a preferred configuration of the fixing clip is provided with blade-like edges (cutting edges) which cut into the receiving element and/or the plug-in element during insertion between the plug-in element and the receiving element, in order to establish a positive connection between the receiving element and the plug-in element. It has proven particularly expedient to produce these cutting edges by bending the outer edges of the longitudinal limbs outwards.
In another advantageous configuration, the fixing clip is provided with means for fixing in the receiving element in various installation positions. In the simplest version, these means have at least one snap-in lug, provided on the receiving element, which can be integrally moulded on the receiving element, and at least one recess, provided on the fixing clip, which this snap-in lug engages. It is particularly advantageous if a recess for the snap-in lug is provided both in the pre-assembly position and in the position for fixing in the final condition. In the pre-assembly position, the snap-in lug engaging the recess prevents the fixing clip from unintentionally falling out of the receiving element. In the final, assembled position, the snap-in lug locks the fixing clip in the desired position.
The snap-in lug can be integrally moulded on the elements.